It was supposed to be a simple mission to update British nationals in Paris about their rights after Brexit. The setting was the 18th-century embassy building, the backdrop to centuries of British diplomacy.

Instead Edward Llewellyn, the British ambassador, was subjected to a two-hour roasting by angry British nationals.

“I went there seeking reassurance and I came away terrified about my future,” Ian Fox, a senior executive at an internationally renowned consumer brand in Paris, told the Guardian after the meeting.

Lord Llewellyn, who was formerly David Cameron’s chief of staff, started out with a prepared speech about the “considerable progress” Brexit negotiators had made, explaining how he understood their “anxieties and concerns”.

But he ended up being heckled and laughed at when he told them Theresa May had prioritised their rights.

“Feel the temperature in the room,” one man shouted.

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Asked if there would be a second referendum, Llewellyn was unequivocal. “There is not going to be a second referendum,” he said. “A second referendum is not the government policy.” This drew gasps of surprise from the audience as it is a political, rather than diplomatic, question.

One woman wanted to know about inheritance law for children born in France and when the Department for Exiting the European Union official told her it was not within “his scope”, she interrupted: “Just say you don’t know.”

She also wanted answers about the future EU research funding rights for a PhD student born to British parents in France, but now studying in London. Would he continue to get funding if he returned to France?

Afterwards she said many felt the only way to not be stripped of rights was to get French nationality.

One woman, who has already made the decision to get a second passport, told the ambassador: “I feel betrayed, but luckily I have a lifeboat, by blood I have a right to have Spanish nationality, but I have to give up my British passport.”

One man, married to a New Zealander, expressed fury that the rights of his family including children born in New Zealand but now living in France, had been thrown up in the air.

“You say May is looking after our interests,” he told the ambassador. “If she is stripping us of our rights, that is demonstrably false. She is happy to flush my rights down the toilet as long as it saves the Tory party.”

After the meeting, he told the Guardian: “I have a lot of respect for those that were fronting up for the UK government. Theirs is a difficult job. However, they should not have tried to put a gloss on things and suggest that May and the UK government is fighting for us. Whatever they are doing can only be considered making the best of a very bad job indeed.”

About 60 British nationals went to the “outreach” meeting on Monday night, armed with detailed questions about their rights, the rights of their children to remain EU citizens, and freedom to continue working across Europe.

The impact of Brexit on their lives was exposed by the detail. What about future spouses? What if they fall in love with a French man or woman? Can they go back to Britain with them? What about assets, and inheritance rights for children born in France?

One woman asked what would happen if she had a child born after 31 December 2020, when Britain exits the EU.

There are an estimated 100,000 British nationals in France and, like many of the estimated 1 million Britons settled in other EU countries, chief among their concerns are the end of freedom of movement after Brexit and employment rights.

British people will become third country nationals after Brexit. The British officials did not have a good answer for one man who asked how Britons would be treated when national law in some countries dictates that priority is given to EU nationals in employment, barring UK nationals from automatic consideration for jobs in the EU post-2020.

“I felt really angry after last night’s meeting,” said Fox. “They don’t seem to be taking us seriously. ”

The ambassador said he would feed the concerns raised back to the government and would hold more outreach events in future. “There are issues that are not resolved,” he said, adding there were “grounds for confidence that we will reach an agreement” encompassing all the rights being sought.